1. Field of the Invention
The present invention relates to a fluorescent lighting device, and in particular, to a lighting device including a fluorescent discharge tube and a resistance ballast, such as an incandescent bulb, for the discharge tube.
According to the recent need for the economy of power, the efficiency of a fluorescent discharge tube has been noted compared with an incandescent bulb for room illumination or commercial display. The color rendering of the fluorescent discharge tube has been improved to provide emission from the fluorescent tube having a natural color or as natural as the incandescent bulb. In view of this improvement in the color rendering, the use of the fluorescent discharge tube in place of the incandescent bulb has been made easier.
There is much difference between the shape of an incandescent bulb lighting device and a fluorescent discharge tube lighting device because of differences in the light sources and the igniting devices. Selection of them has therefore been made according to the place and purpose of use. The achievement of interchangeability between the two lighting devices has not been easy.
In order to use a fluorescent lighting device in place of an incandescent bulb, an independent means for connection, etc. must be provided. For example, additional wiring is required. If it is possible to use the fluorescent discharge tube with the ordinary incandescent bulb illuminating device, demand for the fluorescent discharge tube will increase, which is advantageous for the economy of power.
In some fluorescent discharge tubes, preheating of the discharge electrodes included therein is necessary for starting. In order to stably ignite the preheating type fluorescent discharge tube, it is necessary to include a preheating current control means within the power supply circuit for ignition. As such means, a choke ballast system has been employed using a choke coil for the stabilizer. Other than this system, the resistance ballast system using a resistor wire or an incandescent bulb is known.
In order to ignite a fluorescent discharge tube of this type, it is necessary to include a preheating circuit for preheating the discharge electrodes of the discharge tube before starting the discharge and also a kick voltage generator circuit for obtaining a high starting voltage.
2. Description of the Prior Art
In the preheating circuit, it is necessary to use switching means for closing the current circuit to supply current to the filaments of the discharge electrodes for a very short period at the initial stage of the igniting operation. A glow bulb has been used for this switching means. Also, a manual switch has been used for a desk electric stand, etc. which can be manually controlled.
According to the choke ballast system, a high voltage resulting from the self-inductance of the stabilizer caused by the cut-off of the current at the end of the preheating operation has been used in the kick voltage generating circuit. On the other hand, according to the resistance ballast system, a high voltage generator circuit, such as a transistor inverter has been separately provided. For a small discharge tube less than 20 W, simple means has been proposed in which the line voltage is directly applied to a conductor provided in the vicinity of the outer wall of the discharge tube.
These ballasts are used to assure a stable tube current and proper preheating current. The above mentioned choke ballast system meets these demands. However, a wide inner space within the body is required for mounting the stabilizer, etc. In order to protect the fluorescent tube against the heat generated by the chalk coils, the fluorescent tube must be separated from the choke coils. The structure of the device itself is therefore limited and there is less freedom in the design of the device. With the heavy choke coils, the weight of the entire device becomes greater. Further, there are problems due to the rather loud hum noises generated by the stabilizer.
On the other hand, in the resistance ballast system, the above problems due to the stabilizer are solved, and in particular, when an incandescent bulb is used as the ballast, the bulb itself emits light, which is advantageous in the improving of the color rendering. The power factor of the device and efficiency are also improved. Also, the bulb filament of the incandescent bulb can protect the fluorescent tube against the abnormal circuit current.
The resistance ballast system requires a kick voltage generator circuit, which detects the voltage between the discharge electrodes at the end of the preheating operation and applys a high voltage between the discharge electrodes to start the discharge therebetween. While the discharge continues, the generating operation must be stopped to prevent the consumption of power and to stabilize the discharge current (the tube current). In order to fulfil this condition of operation, complicated electronic circuits have been required, and this has resulted in a higher production cost.